Depression of sulfide zinc minerals from concentrates and ores



Patented Nov. 24, 1953 DEPRESSION F SULFIDE ZINC MINERALS FROM CONCENTRATES AND ORES Charles Francis Allen, Stamford, Conn., Worth Martin Fitzsimmons, Sacramento, Calif., and Robert Ben Booth, Stamford,- Conn., assignors to American Cyanamid Company, New York, N. Y., a corporation of Maine No Drawing. Application September 5, 1952, Serial No. 308,157

8 Claims. (CL 209-167) This invention relates to an improved process of depressing sulfides of zinc or sulfides of zinc and iron from ores or concentrates containing them, together with sulfides of lead.

In the beneficiation of lead-zinc ores by froth flotation, it has long been customary to use reagents for the depression of zinc sulfides. The customary reagent combination is an alkali or alkaline-earth metal cyanide used alone or in combination with zinc sulfate. The most common cyanide used is impure calcium cyanide obtained by electric furnace reaction of calcium cyanamid with carbon and sold under the brand name of Aero Brand Cyanide by the American Cyanamid Company.

According to the present invention, we have found that if ammoniated zinc cyanide complex is used, in which the ammonia is attached by non-ionic linkages or covalent linkages, a much more efficient depression of zinc, or zinc and iron, sulfides is obtained. It should be understood that in order to obtain the advantages of the present invention, there must bean actual ammonia complex, for ionically linked amonia, such as, for example, in the compound ammonium zinc cyanide, does not show the improved results which are possible by means of the present in vention. It is not known why the ammonia must be bound covalently, or in the form of a complex, and, accordingly, the present invention is not limited to any theory as to why the improved results are obtained.

It is an advantage that the complex of the present invention may be made by any suitable method; thus, for example, it is possible to react a zinc salt with ammonia to ammoniate it and then mix this with an ordinary cyanide, such as a cyanide of an alkali or an alkaline-earth metal. It is also possible to use a mixture of ammonia or ammonium hydroxide, soluble cyanide and zinc salt; and they will react together to form the complex ammonia compound. A third method involves ammoniating a soluble cyanide and then mixing it with a zinc salt. Finally, the fourth method which is preferred because of its cheapness and because of the fact that the complex produced is the most active, involves ammoniating preformed zinc cyanide. The proportions of ingredients are not critical. It is desirable to operate with equimolal amounts of the metal and cyanide. However, the amount of ammonia may vary widely and is usually determined by the amount of ammonia which is taken up either by the metal salt or by the cyanide or, in the case of the last method, by the zinc cyanide.

2 I The amount of depressant used varies widely, from somewhat less than a pound to ten pounds or more per ton of flotation feed. As in the case of most froth flotations of ores, the amount will vary for optimum results with different ores and concentrates.

Another advantage of the present invention is encountered in the case where the ore contains some precious metals; for example, where an ore may contain sulfides of lead and zinc associated with auriferrous pyrite. The complex ammoniated zinc cyanide shows remarkably little solvent action for precious metals and, therefore, the loss due to solution of any gold contained in pyrites is kept to a minimum. This additional advantage is of considerable economic importance in the case of ores and concentrates, where the precious metal content is suflicient to be of economic significance. It is possible to use the present invention in the froth flotation of raw ore feed and in the case of metals containing auriferrous pyrite, this is often desirable. On the other hand, it is perfectly feasible to produce concentrates containing both lead and zinc sulfides and to treat these concentrates by the process of the present invention. In general, treatment of concentrates is the preferred method because of economies in the use of the depressant.

It is another advantage of the present invention that the flotation operation is not otherwise affected except that a diiierent depressant is used. No critical operating procedures are required and no new techniques need be learned. In general, the other conditions of the froth flotation operation are exactly the same as when alkali or alkaline-earth metal cyanides are used; thus, the best sulfide collector and frother for the particular ore will be employed when the process of the present invention is used, just as in the old process.

The invention will be described in greater detail in conjunction with the following specific examples, in which the parts are by weight unless otherwise specified.

EXAMPLE 1 An ore containing lead, zinc and iron was floated with 0.10 lb./ton of a mixture of sodium mercaptobenzothiazcle and sodium disec.-butyldithiophosphate and 0.06 lb./ton of a frother comprising a. 6 carbon atom paraflin alcohol to produce a rougher concentrate which was cleaned without the addition of further promoter. This cleaned concentrate, that assayed approximately 28.0% Pb, 32.0% Zn and 35.1% Fe was conditioned for 1 minute with sodium cyanide equal to pounds per ton of concentrate and zinc sulfate equal to 10.0 pounds per ton of concentrate. A lead concentrate was then removed by flotation for a period of 4 minutes. The combination of sodium cyanide and zinc sulfate was inefiective in depressing zinc and iron sulfide minerals during the lead flotation. This test was repeated twice, once using only sodium cyanide in an amount equal to 5 pounds per ton of concentrate and another time using the zinc and cyanide equivalents of the first test but in the form of zinc cyanide ammoniate. The latter test, in which zinc cyanide ammoniate was used, was much more efiective in depressing lead and iron sulfides during lead flotation. The metallurgical results obtained in these tests follow:

Cleaned concentrate Assay, Percent Distribution fi Pb Zn 1 Fe Pb Zn Fe 86. 8 29.3 32.3 4.8 97. T 89.9 81. 7 58. 4 42. 4 27. 6 1. 9 83. 0 57. 2 21. 1 40. 2 56. 6 16. l 2. 6 82. l 20. 6 20. 4

Tailing Assay, Percent Distribution Pb Zn Fe Pb Zn 1 Fe 1 Test 1 13. 2 4. 6 23. 8 7. 1 2. 3 10. 1 i 18. 3 Test 2 41. 6 12. 2 29. 0 9. 9 l7. 0 42. 8 78. 8 Test- 3 59. 8 8. 3 41. 6 6. 8 l7. 9 79. 4 70. 6

Reagents lbs./ ton Zinc Cyanide Ammoniate Test3 I ..I "ifs It will be noted that a very marked improvement in zinc depression results, the clean concentrate containing as much zinc when the ammoniated zinc cyanide of the present invention is used. Depression of pyrite is not greatly improved, but the depression is just as good as with the cyanide employed according to the prior art; in other words, a great improvement in zinc depression is obtained without any corresponding loss in pyrite depression.

EXAMPLE 2 An ore containing lead, zinc and iron was floated with 0.5 lb./ton of copper sulfate, 0.1 lb./ton of sodium sec.-butylxanthate and 0.12 lb./ton of the frother of Example 1. The ore was floated to produce a rougher concentrate which was cleaned with 0.04 lb./ton of the frother of Example 1, producing a cleaner concentrate which assayed approximately 25.4% Pb, 20.1% Zn and 7.8% Fe was conditioned for 1 minute with approximately 5.5 pounds per ton of zinc cyanide ammoniate and a lead concentrate was removed by flotation for a period of 3 minutes. The lead concentrate assayed 45.6% Ph, 9.2% Zn and 3.1% Fe and recovered 97.9% of the lead, 249% of the zinc and 21.6% of the iron in the bulk concentrate.

EXAMPLE 3 A lead-zinc ore from Mexico which assayed approximately 10.0% Pb, 4.1% Zn and 7.1% Fe was ground with 5.0 pounds per ton of hydrated lime and 2.0 pounds per ton of tetrasodium pyrophosphate. The ground pulp was conditioned for 1 minute with 2.0 pounds per ton of Aero Brand Cyanide, 2.0 pounds per ton of zinc sulfate, 0.07 pound per ton of a mixture of sodium salts of mercaptobenzothiazole and di-sec.- butylthiophosphate, and 0.03 pound per ton of methyl isobutyl carbinol. A lead concentrate was then floated for a period of 4 minutes and 0.03 pound per ton of methyl isobutyl carbinol was added during flotation. In this test 93.5% of the lead, 24.1% of the zinc and 11.1% of the iron was recovered in the lead concentrate. Another test was run which was identical with this first test except that the zinc and cyanide equivalents were used in the form of zinc cyanide ammoniate which was aproximately 1.5 pounds per ton of zinc cyanide ammoniate. In this test 93.3% of the lead, 18.6% of the zinc and 9.4% of the iron was recovered in the rougher concentrate. The metallurgical results obtained in these tests follow:

Cleaned concentrate A sample of lead-zinc-silver ore from Central America was ground with hydrated lime equal to 2.0 lb./ton and 1.0 lb./ton of zinc cyanide ammoniate as well as 0.08 lb./ton of a mixture of sodium salts of mercaptobenzothiazole and di-sec.-butylthiophosphate. The ground pulp was conditioned for 1 minute with 0.10% of pine oil and 0.02 pound per ton of methyl isobutyl carbinol. The rougher lead concentrate assayed 42.4% Pb, 14.1% Zn and 75.2 ounces of silver per ton of ore. This product recovered 94.7% of the total lead, 28.3% of the total zinc and 82.2% of the total silver in the ore.

It will be noted that not only was there very effective depression of zinc, but the losses of silver are very slight.

EXAMPLE 5 A sample of lead-zinc-silver ore from Canada which assayed approximately 3.3% Pb, 5.4% Zn 5 and 16.5 ounces of silver per ton of ore was ground with 0.025 pound per ton of zinc cyanide ammoniate. The ground pulp was conditioned for 1 minute with 0.04 pound per ton of sodium ethyl xanthate and 0.06 pound per ton of methyl isobutyl carbinol. A lead concentrate was then removed by lead flotation for 2 minutes. During the flotation period 0.02 pound per ton of sodium ethyl xanthate and 0.03 pound per ton of methyl isobutyl carbinol were added. The rougher lead concentrate produced in this test assayed 42.0% Pb, 3.7% Zn and 140.7 ounces of silver per ton. This concentrate recovered 93.6% of the total lead, 5.1% of the total zinc and 63.0% of the silver in the ore.

It will be noted that not only was there very effective depression of zinc, but the losses of silver are very slight,

EXAMPLE 6 A sample of lead-zinc-silver from Colorado which assayed approximately 3.8% Pb, 4.3% Zn, 5.7% Fe and 7.0 ounces of silver per ton was ground with 4.0 lb./ton of soda ash. The ground pulp was conditioned for 1 minute with 0.07 lb./ ton of a mixture of sodium salts of mercapto benzothiazole and di-sec.-butylthiophosphate, and 1.0 pound per ton of zinc cyanide ammoniate and a lead concentrate which was produced assayed 36.2% Pb, 12.4% Zn, 13.2% Fe and 49.0 ounces of silver per ton. This product recovered 78.6% of the total lead, 23.7% of the total zinc, and 19.2% of the iron, as well as 58.0% of the silver in the ore. It will be noted that not only was there very effective depression of zinc but the losses of silver are very slight.

We claim:

1. A process of selectively depressing zinc and iron sulfides in the froth flotation of ores and concentrates containing lead and zinc sulfides, which comprises effecting froth flotation in the presence of an effective amount of collector for lead sulfide and an eifective amount of a depres sant containing cyanide radical, zinc and non- V ionically linked ammonia.

2. A process according to claim 1 in which the depressant is prepared by ammoniating preformed zinc cyanide.

3. A process according to claim 2 in which the ore or concentrate contains only sulfides of zinc in adition to the lead sulfides and substantially free from sulfides of iron.

4. A process according to claim '1 in which the ore contains only sulfides of zinc in addition to the lead sulfides and substantially free from sulfides of iron.

5. A process according to claim 1 in which the ore contains sulfides of lead, zinc, and iron and the latter two are depressed.

6. A process according to claim 5 in which the depressant is prepared by ammoniating preformed zinc cyanide.

7. A process according to claim 1 in which the ore contains sulfides of lead, zinc and iron, and precious metal compounds, and the sulfides of zinc and iron are depressed without substantial solution of the precious metal.

8. A process according to claim 7 in which the depressant is prepared by ammoniating preformed zinc cyanide.

CHARLES FRANCIS ALLEN. WORTH MARTIN FITZSIMMONS. ROBERT BEN BOOTH.

No references cited. 

1. A PROCESS OF SELECTIVELY DEPRESSING ZINC AND IRON SULFIDES IN THE FROTH FLOTATION OF ORES AND CONCENTRATES CONTAINING LEAD AND ZINC SULFIDES, WHICH COMPRISES EFFECTING FROTH FLOTATION IN THE PRESENCE OF AN EFFECTIVE AMOUNT OF COLLECTOR FOR LEAD SULFIDE AND AN EFFECTIVE AMOUNT OF A DEPRESSANT CONTAINING CYANIDE RADICAL, ZINC AND NONIONICALLY LINKED AMMONIA. 